This invention relates to voltage regulators and, more particularly, to a voltage regulator of the type that includes a bandgap reference.
Bandgap voltage references are used extensively in high-performance analog and digital circuits. In these circuits, the regulators serve to establish precise voltage levels at specified internal and/or output node points. By means of such a regulator, the voltage at a node point can be maintained relatively constant even as changes occur in temperature, supply voltage and load current.
Known bandgap voltage regulators comprise a bandgap reference combined with an error amplifier which often contains a current mirror. Some of these combinations which include both PNP- and NPN-type transistors exhibit excellent operating characteristics.
In some technologically advanced processes utilized to fabricate high-speed silicon or heterojunction bipolar devices, it is possible to make excellent NPN transistors. But the PNP transistors made by such processes often exhibit low current gain, low breakdown voltage or poor V.sub.BE matching. Hence, for such a fabrication process it is advantageous to design regulators that include only NPN transistors.
Bandgap voltage regulators made of only NPN transistors have been proposed. But priorly known all-NPN-transistors regulators tend to be relatively complicated and to exhibit relatively poor operating characteristics.
Accordingly, efforts have been directed at trying to devise a relatively simple bandgap voltage regulator made of only NPN transistors that would provide better performance than heretofore realized with an all-NPN-transistor design. It was recognized that these efforts if successful would contribute significantly to the realization of high-performance integrated circuits fabricated by high-speed bipolar processes.